The Average Internal Rate of Return (AIRR) approach in the article shows that projects are linked to a return function, not just one return rate. Any rate of return definition in the past or future is a type of AIRR. When choosing between projects, the AIRR acceptability criterion can be used for the incremental project. AIRR easily gives the rate of return on the initial investment, unlike IRR which only gives the rate of return on the total capital implied by IRR.